The present invention relates to a plant intended to generate heat from the combustion of a fuel containing notably sulfur and nitrogen, with limited emissions of sulfur oxides.
Several publications describe how to reduce the emissions of sulfur oxide and more specifically of sulfur dioxide coming from a boiler of the type cited above.
These boilers conventionally comprise a combustion chamber, at least one convective exchange zone, a desulfurization chamber comprising at least one means for injecting an absorbent and communicating with a first convective exchange zone, a first separation chamber connected to said first convective exchange zone, said separation chamber having at least one outlet for the spent absorbent and an outlet for the depolluted gases.
Patent application FR-A-2,636,720, discloses a boiler known as "desulfurizing" boiler and comprising a desulfurization chamber arranged between a combustion chamber (upstream) and a heat recovery chamber (downstream), the assembly having the advantage of being compact since the desulfurization chamber is integrated between the combustion chamber and the heat recovery chamber.
French Patent application FR-90/08,311 is an improvement of the previous application since it provides, in order to keep a constant temperature in the desulfurization chamber, whatever the variations of the rating of the boiler may be, for recycling of a part of the absorbent used, towards the inlet of the desulfurization chamber, the rate of flow of this recycling being furthermore controlled.
The absorbent injected in these boilers mainly consists of a calcic matter which is sent, after partly sulfurizing, towards a storage hopper.
This type of "desulfurizing" boiler therefore leads to the production of not insignificant amounts of spent calcic absorbent, i.e. desulfated. In the end, the amount of discharged absorbent may pose storage problems, which is quite understandable.
The calcic absorbents can represent each year several millions, and even several ten millions of tons of waste to be stocked, hence a storage volume problem. Besides, during the storage thereof, the absorbents can be wetted, washed and therefore release the metallic pollutants they contain, thereby polluting the phreatic surface sheets.